1. Field of the Invention
The present invention relates to an electrically conductive material suitably used for a flat panel display (FPD) and a current drive type light emitting device (LED).
2. Discussion of Background
Heretofore, for a FPD such as a liquid crystal display device, a plasma display and an organic LED and for a solar battery, a substrate provided with a transparent electrode film as a transparent electrode has been used. As a material for the transparent electrode film, indium oxide type, zinc oxide type and tin oxide type are known. ITO (tin-doped indium oxide) which is of indium oxide type is particularly famous and widely used As reasons why ITO is widely used, its low resistance and favorable patterning properties are mentioned, but in view of effective utilization of resources, development of a material which will replace indium is desired at present.
As a material of the transparent electrode film, as two element i.e. two-dimensional crystals other than the above material, a TiO2 type material has been known. For example, by doping anatase-form TiO2 with several % of Nb, a material having a specific resistance in a figure in 1E-4 (1×10−4) Ω·cm can be prepared (for example, Non-Patent Document 1). Further, as three element i.e. three-dimensional crystals, ZnSnO3 and Zn2SnO4 have been known to be a transparent electrode film, and materials having specific resistances in a figure in 1E-3 Ω·cm and 1E-2 Ω·cm, respectively, can be prepared by preparation under appropriate film formation conditions.
However, most of these materials are materials only exhibiting n-type electrical conductivity. In the field of an organic LED and a solar battery, there is a need for improvement of power generation efficiency or luminous efficiency by injecting holes to a film made of a material having p-type electrical conductivity directly from a transparent electrode. However, many materials including the above materials exhibit only n-type electrical conductivity, and it has been difficult to prepare a material exhibiting p-type electrical conductivity. Further, a three-dimensional transparent electrically conductive tin oxide film containing tin oxide and tungsten oxide has been known (for example, Patent Document 1). The transparent electrically conductive tin oxide film contains tin as the main component and tungsten as an additive, and is formed by applying a solution of a mixture prepared by adding a tungsten compound to a tin compound, to a heated transparent substrate by spraying. Although it may be possible to obtain favorable electrical conductivity by such a method, n-type and p-type materials cannot selectively be formed.
Non-Patent Document 1: The 65th Meeting of the Japan Society of Applied Physics, Abstract Papers No. 2, p. 530, “New transparent metals: Nb-doped anatase TiO2”
Patent Document 1: JP-A-8-64035